The present invention relates to a rotary blower, such as a supercharger, and a torsion damping or isolating mechanism therefor. More specifically, the invention relates to a combination pulley and isolator for reducing audible noise of timing gears in a backflow-type supercharger driven by an internal combustion engine.
Rotary blowers of the backflow-type, particularly Roots-type blowers, have been characterized by noisy operation. The noise generated by Roots-type blowers may be classified as either: (a) solid borne noise caused by clashing of components subjected to fluctuating loads; or (b) fluid borne noise caused by fluid flow characteristics, such as rapid changes in fluid velocity, the "fluid", in the case of a supercharger, comprising air. The present invention is concerned with the former, i.e., solid borne noise, and more specifically, noise caused by timing gear rattle.
The timing gears of Roots-type blowers may produce an objectionable gear rattle when the meshed teeth of the gears are substantially unloaded. Such unloaded conditions occur during non-supercharging, low engine speed modes of operation. The gear rattle may be mitigated by a torsion damping mechanism having a low torque transmitting capacity, low rate spring, as well as forward and reverse stops, the forward stop being operative in case of an abrupt increase in engine speed, or in the input drive torque, and the reverse stop being operative in case of an abrupt change in input speed, such as in the case of engine shut down. Such a torsion damping mechanism is illustrated and described in U.S. Pat. No. 4,944,278, assigned to the assignee of the present invention and incorporated herein by reference.
Although the prior art torsion damping mechanism has been generally satisfactory in operation, it has added substantially to the cost of the blower. For example, its location immediately forward of the timing gear means that, in addition to the two rotor shafts, there must also be a third shaft, transmitting input torque from the supercharger pulley to the input of the torsion damping mechanism. The third shaft requires a bearing, disposed toward each end of the third shaft, the third shaft and the bearings thus adding to the overall axial length, complexity, and cost of the input portion of the blower.